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How to scan with two paralel laser line?

ozgur84

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Hello everybody,

I have been dealing with a laser scanner project for a while which works with triangulation method (david laser scanner). However, lately I have seen another application in mythbusters tv show as well as the announcement of makerbot digitizer

Here you can watch the video and see what I mean

or something like this

both applications do not use a right angle calibration grids or backgrounds(except the black cloth behind).

This technique is also used in CAT scanners in medical imaging.

Does anybody know how this technique works? or can you suggest a porject example from which I grab some ideas or keywords.

(Yes I have already made a google search)

regards
 
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DrSid

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So the object rotates, and the camera extracts the laser line projected on the object from the video. From one frame you get one profile. If you then place the profiles into virtual space at relevant rotations, you'll get the object. It would only work for objects which do not have holes inside, for example you wouldn't be able to scan inside of a cup.
It looks like it uses 45 degree angle, so camera sees the laser line well all the time. The line basically shows profile of the object at any given time. You then have to project the line onto plane of the laser .. which will correct for both perspective and profile shortening due the 45 degree angle .. and you get the points in virtual space. Sure, you will have to skin then later, but that is same for all 3D scanners. It should work with basically any angle, as long as camera sees the line. The angle should well though, so the distance from axis and perspective are corrected correctly.
Looks very simple. Now I want to build it. :thinking: If you are interested, I guess I could even provide all math needed, but be warned, you will need vectors and matrices :umbrella:

Btw. CAT works a bit differently. Yes, it rotates around. It also gets profiles over time. But it does not only scan the surface of the object, it scans densities inside. Result is not a surface of an object, but basically 3D volume map, where every point in space has it's density scanned. That is done by software analysis from the density profiles, that why it is called computer tomography after all.
This laser scanner is way simpler.
 
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ozgur84

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So the object rotates, and the camera extracts the laser line projected on the object from the video. From one frame you get one profile. If you then place the profiles into virtual space at relevant rotations, you'll get the object. It would only work for objects which do not have holes inside, for example you wouldn't be able to scan inside of a cup.
It looks like it uses 45 degree angle, so camera sees the laser line well all the time. The line basically shows profile of the object at any given time. You then have to project the line onto plane of the laser .. which will correct for both perspective and profile shortening due the 45 degree angle .. and you get the points in virtual space. Sure, you will have to skin then later, but that is same for all 3D scanners. It should work with basically any angle, as long as camera sees the line. The angle should well though, so the distance from axis and perspective are corrected correctly.
Looks very simple. Now I want to build it. :thinking: If you are interested, I guess I could even provide all math needed, but be warned, you will need vectors and matrices :umbrella:

Btw. CAT works a bit differently. Yes, it rotates around. It also gets profiles over time. But it does not only scan the surface of the object, it scans densities inside. Result is not a surface of an object, but basically 3D volume map, where every point in space has it's density scanned. That is done by software analysis from the density profiles, that why it is called computer tomography after all.
This laser scanner is way simpler.
Hey, thanks for the answer it was quite descriptive. I am a physicist, so I think I can handle the math necessary but programming part can be quite hard. I would like to build one too so lets do it together. I know little circutary for motor control and optics.

By the way what I ment abot the CAT scanners, there are two line laser which scan the paitients body just at the enterance of the measurement area apart from the X-Ray scan. I think yok know what I mean:)
 

DrSid

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Hey, thanks for the answer it was quite descriptive. I am a physicist, so I think I can handle the math necessary but programming part can be quite hard. I would like to build one too so lets do it together. I know little circutary for motor control and optics.

By the way what I ment abot the CAT scanners, there are two line laser which scan the paitients body just at the enterance of the measurement area apart from the X-Ray scan. I think yok know what I mean:)
Let's do it together sounds like fun, but unfortunately I would like to NOT to get engaged in yet another project. I think I could handle the programming .. but I can honestly say I don't have time. Of course, all depends on what time frame are we talking about. How fast you would want this. What hardware platform are we talking about .. what output you do require ..

As for CAT, I guess those lasers are for aiming only .. but who knows.
 




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